The invention relates to cationic lipids useful in synthetic gene delivery systems. It relates particularly to amphiphilic cationic lipids having conjugated polyamine groups.
Plasmid based, non-viral gene delivery systems represent a promising approach for the treatment of inherited and acquired diseases, and for the development of a new approach to vaccination.1-8 However, their efficiencies and clinical potencies are limited today due to low level in vitro and in vivo gene product expression.6,9 The commonly used approaches for increasing expression of synthetic gene delivery systems involve either improving the DNA delivery system,3,4,9 or optimizing the DNA sequence at the level of either the promoter, enhancer, intron, or terminator.10-13 
DNA delivery systems include cationic lipids capable of facilitating the transport of biologically active agents, including plasmids, into the cell both in vitro and in vivo, for example, as disclosed in U.S. Pat. No. 4,897,355 to Eppstein et al. and U.S. Pat. No. 5,264,618 to Felgner et al. Synthetic gene delivery systems also comprise the use of cholesterol-based cationic lipids. Lipids such as DC-cholesterol are shown to have both in vivo and in vitro transfection activity4,14-18 and were the first cationic lipid molecules to be used in human gene therapy clinical trials. It is medically and commercially important to develop improved species of cationic lipids having enhanced transport or transfective potency.